Mechanics

Mechanics is an important area of scientific study that helps us understand how things move and change. It comes from the Ancient Greek word for "of machines" and is part of physics. Mechanics looks at how forces affect matter and cause motion. When forces act on objects, they can make the objects move or change position.

People have been thinking about mechanics for a very long time. Ancient thinkers like Aristotle and Archimedes wrote about it. Later, during a time called the early modern period, scientists such as Galileo Galilei, Johannes Kepler, Christiaan Huygens, and Isaac Newton helped create what we now call classical mechanics.

In the 1900s, new discoveries made scientists rethink some ideas. This led to new ways of understanding mechanics, such as relativistic mechanics and quantum mechanics. These help explain how things move and behave in ways that were not possible before.

History

Main articles: History of classical mechanics and History of quantum mechanics

Antiquity

Main article: Aristotelian mechanics

Ancient Greek philosophers were among the first to suggest that rules shape how nature works. The main idea about how things move in those times was Aristotelian mechanics, though another idea appears in the pseudo-Aristotelian Mechanical Problems, perhaps written by one of Aristotle’s followers.

Some Greeks used math more to study objects that stay still or move. This might have started with the work of the Pythagorean Archytas. Examples include pseudo-Euclid (On the Balance), Archimedes (On the Equilibrium of Planes, On Floating Bodies), Hero (Mechanica), and Pappus (Collection, Book VIII).

Medieval age

Main article: Theory of impetus

During the Middle Ages, people thought about and changed Aristotle’s ideas. One big question was how things fly through the air, talked about by Hipparchus and John Philoponus in the 6th century.

The Persian Islamic scholar Ibn Sīnā wrote about how things move in The Book of Healing around 1020. He said that when you throw something, it keeps moving because of a push called “impetus.” This push slowly goes away because of things like air resistance. Ibn Sina also said that an object keeps moving until something stops it, like if there were no air.

Around the 1100s, a Jewish scholar named Hibat Allah Abu'l-Barakat al-Baghdaadi said that when something falls, it speeds up because of its own nature. Later, a French priest named Jean Buridan in the 1300s created the theory of impetus. This helped lead to today’s ideas about how things move without being pushed, speed, and how fast they speed up. Scholars in England, called the Oxford Calculators, also studied how things fall.

Early modern age

Two important people from the 1600s were Galileo Galilei and Isaac Newton. Galileo’s last big book on how things move, Two New Sciences, came out in 1638. Newton’s book from 1687, Philosophiæ Naturalis Principia Mathematica, used new math called calculus to explain mechanics clearly. This became known as Newtonian mechanics.

Modern age

Two big advances in mechanics happened in the 1900s: Einstein’s idea of general relativity and quantum mechanics. These built on ideas from the 1800s. Also, in the second half of the 1900s, scientists made progress in understanding how solid and liquid materials behave under different forces.

Types of mechanical bodies

The word body can describe many different things, like particles, projectiles, spacecraft, stars, parts of machinery, parts of solids, and parts of fluids such as gases and liquids.

In mechanics, we study different kinds of bodies. Particles are very simple and have no known inner structure. Rigid bodies have a fixed shape and size but can move in simple ways, like turning in space. Other bodies can change shape a little, like elastic materials, or a lot, like fluids. These ideas are studied in both classical and quantum mechanics. For example, the movement of a spacecraft in its orbit and rotation is explained by classical mechanics, while the movements inside an atomic nucleus are explained by quantum mechanics.

Sub-disciplines

The three main areas of mechanics are Classical, Quantum, and Relativistic mechanics.

Classical

Classical mechanics studies how objects move and the forces that affect them. It includes Newtonian mechanics, which looks at motion and forces, and analytical mechanics, which focuses on energy. Other parts of classical mechanics cover the movement of planets and stars, the behavior of solids and fluids, and the study of sound.

Quantum

Quantum mechanics deals with the behavior of very small particles, like atoms and electrons. It includes different ways to describe these particles and their movements. Quantum mechanics developed later than classical mechanics and is needed to explain things that happen at very small scales.

Relativistic

Relativistic mechanics looks at how objects move when they travel very fast, close to the speed of light. It builds on the work of Newton and Galileo but uses ideas from Einstein's theories of relativity. At these high speeds, the rules of motion change significantly.

Main article: Classical mechanics

Main article: Quantum mechanics

Main article: Relativistic mechanics

Professional organizations

There are groups that bring together people who study and work with mechanics. Some of these groups include the Applied Mechanics Division, American Society of Mechanical Engineers, Fluid Dynamics Division of the American Physical Society, the Society for Experimental Mechanics, and the International Union of Theoretical and Applied Mechanics. These organizations help scientists and engineers share their ideas and discoveries.